This invention generally relates to digital data processing systems. More specifically it relates to a processor for use in such data processing systems.
A digital data processing system comprises three basic elements: namely, a memory element, an input-output element and a processor element. The memory element stores information in addressable storage locations. This information includes data and instructions for processing the data. The processor element transfers information from the memory element. It interprets the incoming information as either data or an instruction. An instruction includes an operation code that specifies, in coded form, the operation to be performed by the processor. An instruction may also include information that specifies one or more operands. The information that specifies an operand is called an operand specifier.
The various functions that a processor performs in response to the operation code code in a given instruction might be quite simple or very complex. Some of the more complex operations are found in instructions generally known as floating point instructions that perform arithmetic operations using floating point numbers. In the past different approaches have been utilized for processing floating point numbers in accordance with such instructions. In one approach the processor itself is constructed to process the floating point instructions in the same manner as other instructions. With this approach, however, the processor complexity is increased over processors that do not have that capability. In many applications the added complexity is not justified by the end use of the processor.
Another approach utilizes optional circuitry that readily connects to the processor to process the floating point instructions directly. This offers the advantage that the processor complexity need not be greatly increased in normal applications. However, it does require the added cost of the optional circuitry if any of the instructions is to be processes because the processor itself does not have the capability.
With the advent of microprocessor controlled data processing systems, it has been possible to implement floating point instructions within a processor without unduly increasing its overall cost. However, these implementations usually require significant periods of time in order to complete the processing period. While the long processing times may be acceptable when such instructions are processed only occassionally, the times can become unacceptable if such instructions are used repetitively.
Therefore, it is an object of this invention to provide a unit for processing specific types of instructions.
Still another object of this invention is to provide a unit for connection to a processor in a data processing system that utilizes the processor to obtain operands and then processes the operands.